In an episode that seems more like a journey into outer space than a voyage into our global waters, Sir David Attenborough introduces us to the remarkable and often downright bizarre sea life that dwells in the deepest areas of our oceans, where the lack of sunlight and high pressure results in only the toughest – and oddest – surviving.
High on the weirdness scale is the sea toad (a fish with legs!) and a barreleye fish that has a transparent head so it can see everything above it.
But prepare to be terrified by the creepy fangtooth, with its huge teeth and pressure sensors on its body that sense when any prey is nearby.
There’s also remarkable footage of volcanic hot-spots, where life still thrives.